Synthesis and transient photocurrent behavior of Zn-doped In2O3 nanorods

Accepted Manuscript Title: Synthesis and transient photocurrent behavior of Zn-doped In2 O3 nanorods Authors: Asghar Shokohmanesh, Farid Jamli-Sheini PII: DOI: Reference:

S0924-4247(16)30806-8 http://dx.doi.org/doi:10.1016/j.sna.2017.08.010 SNA 10264

To appear in:

Sensors and Actuators A

Received date: Revised date: Accepted date:

29-10-2016 2-5-2017 4-8-2017

Please cite this article as: Asghar Shokohmanesh, Farid Jamli-Sheini, Synthesis and transient photocurrent behavior of Zn-doped In2O3 nanorods, Sensors and Actuators: A Physicalhttp://dx.doi.org/10.1016/j.sna.2017.08.010 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Synthesis and transient photocurrent behavior of Zndoped In2O3 nanorods

Asghar Shokohmanesh 1, Farid Jamli-Sheini 2,*

1

Department of Materials Science and Engineering, Ahvaz Branch, Islamic Azad University,

Ahvaz, Iran 2

Advanced Surface Engineering and Nano Materials Research Center, Department of

Physics, Ahvaz Branch, Islamic Azad University, Ahvaz, Iran

*Corresponding

author:

E-mail: [email protected] , [email protected] Telephone No: +98 - 61 - 33348420 - 24 Fax No. : +98 - 61 - 33329200

Graphical abstract

1

Highlights  Zn-doped In2O3 nanorods synthesized by electrochemical method.  The effect of Zn doping on physical property of the deposited films was studied.  High photocurrent density with transient behavior of the films was observed.

Abstract Electrochemical deposition method has been used to synthesize un- and Zn-doped indium oxide (In2O3) thin films. The results of the diffraction pattern analysis confirmed the presence of In2O3 phase in two crystal structure of cubic and rhombohedral. Scanning electron microscope images show presence of nanorods and with the addition of zinc dopant does not change the shape of In2O3 thin films, but their size (diameter) is firstly reduced and then increased by increasing the amount of dopants. The photoluminescence spectra also show the presence of emission bands in the visible regions, which is because of oxygen vacancies. Moreover, absorption spectrum indicated an absorption edge in the ultraviolet region with a shift to higher wavelength and also a decrease in the intensity of absorption by adding zinc dopant. The photocurrent plots showed that the specimen doped with lower value of zinc concentration has the highest current efficiency with transient behavior after light stimulation.

Keywords: In2O3 Nanostructures; Electrochemical Deposition; Zinc dopant; Electro-optical Properties

1. Introduction Indium oxide (In2O3) is a compound semiconductor with a direct band gap of 3.6 eV and indirect band gap of 2.6 eV that has been used in light-emitting diodes [1], solar cells [2], gas sensor [3, 4], photovoltaic device [5], anti-reflective coatings [6], etc. So far, several 2

methods have been used to synthesis In2O3 that include thermal evaporation [7, 8], sputtering [9], sol-gel [10, 11], spray pyrolysis [12, 13] electrochemical deposition [14, 15] and so on. Among these methods, electrochemical deposition has many advantages such as low-cost and non-vacuum equipment, easy and high controlling on growth parameters as well as the possibility of growth in a large scale compared to other growth methods. The physical properties of nanostructured semiconductors can be altered by changing their band gap. A desired band gap can be achieved by using a suitable dopant with an effective amount. Various substances have been used as dopants for In2O3 by using different methods [15-17]. The following history can be briefly pointed in terms of using electrochemical deposition technique to grow the nanostructured In2O3. Zheng et al. grew In2O3 nanowire arrays in an alumina membrane. Optical study showed that their optical absorption edge has a red shift compared to the bulk In2O3 and the amount of its shifts depends on the heat treatment after nanowires growth [18]. Xu et al. used DC voltage to obtain In2O3 nanostructures, evaluated films to identify H2S gas, and concluded that In2O3 nanostructures have a high sensitivity to detect this gas [19]. Sharma et al. grew In2O3 thin films to be used as a buffer layer in dye solar cells. Changes in current-voltage density characteristic in both light and dark films indicated that these films have a good performance to use as the host electrode in dye solar cells [2]. In the study conducted by Chu et al., it was found that various forms of In2O3/In(OH)3 nanostructures can be obtained by changing electrochemical deposition method parameters such as temperature, time, concentration and applied potential and growth of these nanostructures, which appeared in oval, cubic and bar shapes, can be controlled [20]. In2O3 thin films were grown and characterized by Henriques et al. using modified electrochemical deposition method. The results of Mott-Schottky plot showed that the mentioned films have n-type conductivity. From the Tauc plots, their optical band gap energy estimated and showed direct band energy of 3.54 eV and indirect band energy of 2.83 eV [21]. Although we introduced several works done by the researchers on the effect of dopant on In2O3 thin films, the investigations of morphological and electro-optical properties are new and useful when it is doped with suitable elements. In this study, it is tried to answer this question that how In2O3 (un- and Zn-doped) films can be synthesized using electrochemical deposition, and what effects does doping have on the electro-optical properties. Therefore, the aim is gaining a good understanding of the impact of dopants on the morphological and electro-optical properties of these films and comparing the obtained results those of previous 3

studies. Accordingly, in this study, the electrochemical deposition method was used to deposit nanostructured In2O3 thin films and its band gap energy engineering has been investigated by using the zinc (Zn) dopant that it has not been investigated with this method.

2. Experimental 2.1. Synthesis. In2O3thin films growth was performed in an electrochemical deposition cell with three electrodes. The electrolyte solution involves a combination of InCl2 (From the company of Merck, 99.99%) and H2O2 at concentration of 0.02 M. In order to make the electrolyte for doping, an aqueous solution of ZnCl2 (From the company of Merck, 99.99%) as a source of dopant with concentrations of 0.002 M (2cc or 2%) and 0.004 M (4cc or 4%). By adding different quantities of this solution (2 and 4 cc) to different beakers, separate experiments were carried out. The electrolyte solution is always stirred during the deposition by the stirrer heater at the constant temperature of 85 °C. The pH of the electrolyte solution was also kept at a value of 3. A fluorine doped tin oxide (FTO)-coated glass substrate (~ 8 Ω/cm2), platinum sheet, and saturated calomel electrode (SCE) (E0 = 0.244 V vs. normal hydrogen electrode (NHE)) served as the working, counter, and reference electrodes, respectively. Substrates and platinum electrode were washed with acetone and ethanol solutions for 10 min in an ultrasonic stirrer to ensure that there is no pollution on them. An electrochemical analyzer controlled by computer (Potentiostat, Autolab, Model A3ut71167) was used to create the cathodic polarization conditions at a voltage of -1.4 volts in the sequence of SCE (SCE, E0 = 0.244 V vs. NHE). The deposition duration was 30 min. After depositing, and removing the specimens from the electrolyte solution, it was gently washed with distilled water and then it was dried in air and prepared for characterization. 2.2. Characterizations. The crystal structure of obtained In2O3 thin films was studied using an X-ray diffraction system (XRD, X'Pert Pro MPD, PANalytical, Cu Kα = 1.5406 Å). In order to study the surface morphology and elemental composition of deposited films, scanning electron microscopy (SEM, VEGA\\TESCAN) imaging and energy dispersive Xray spectroscopy (EDS) were performed with an elemental analyzer attached to the same SEM. Optical properties of thin films were also analyzed using the photoluminescence (PL) analyses and the absorption spectrum. PL analysis was performed at room temperature with a Perkin-Elmer LS55 system and the excitation wavelength of 275 nm in the range of 300-800 nm and the absorption spectrum was also recorded at room temperature using a UV-Vis 4

spectrophotometer model CE-7500. Photocurrent cell were assembled using the deposited films as working electrodes and Pt foil as the counter electrodes, which were sealed in a sandwich cell filled with the electrolyte in a 100 µm thick spacer. The electrolyte liquid was I-/I-3. The photocurrent response and I-V data was measured by the mentioned potentiostat using a 100W xenon lamp as the light source and a switching frequency of 0.05 Hz. C-V characteristics was recorded by a inductance (L)-capacitance (C)-resistance (R) (LCR) meter (LCR-8000G Series-Gwinstek) at frequency of 1 kHz in order to obtain Mott–Schottky plot.

3. Results and Discussion Figure 1 shows the XRD patterns of deposited films for un- and Zn-doped specimens with different concentration of Zn. All of the XRD patterns indicate a set of well-defined diffraction peaks, which are indexed to cubic (JCPDS Card No. 00-006-0416) and rhombohedral (JCPDS Card No. 01-073-1809) [22] of In2O3 and no additional phase caused by a combination of Zn and oxygen (O) are observed in the films. The peak position of diffraction for doped specimens (inset) shifted towards lower angles. This shift is associated with the ionic radius of In and Zn. However, the ionic radius of Zn (0.74 Å) is smaller than the ionic radius of In (0.80 Å) [23] and we should have shift towards larger angles. Therefore, the replacement of some In atoms by Zn atoms in the In sites is expected. Moreover, many Zn atoms were placed in a state of interstitial position and caused applying stress in the In2O3 lattice. This phenomenon is also observed and reported in other studies. Ye et al. reported such shift during doping In2O3 with copper (Cu) and they stated that this is because of the high stress acted on the crystal lattice [21]. Figure 2 shows the SEM images and the EDS spectra of deposited films for un- and Zn-doped specimens with different concentration of Zn. As this figure shows, the un-doped specimen has a rod shape with an average diameter of 32 ± 2 nm. With the addition of 2% Zn dopant, the diameter of the rods has been reduced and it reached to an average of about 19 ± 2 nm. Increasing the amount of Zn dopants to 4%, larger rods with an average diameter of about 37 ± 2 nm will be resulted. By adding Zn dopant, the size of nanostructures is firstly decreased and then increased. The compositions of the films were checked using an EDS analysis, which showed the presence of In and O elements. The atomic percentage of O was decreased (42.83 and 56.39% for 2% and 4% Zn-doped In2O3, respectively) by adding dopant

5

(2.40 and 3.37% for 2% and 4% Zn-doped In2O3, respectively) as compared with un-doped sample. The better stoichiometry for Zn-doped specimens was obtained. Generally, the growth process of In2O3 thin films in the electrochemical deposition method can be explained as in different stages of atomic levels. At first, stable nucleuses of In3+ are formed on the substrate that they have moved from the electrolyte solution toward the cathode. In the next step, these nucleuses, which have a strong tendency to absorb electrons, began to attract anions existing in the electrolyte solution. It is noticeable that applying potential difference causes giving electrons to O atoms through the anode electrode. Therefore, they strongly tend to move toward the cathode electrode where they are absorbed by the cathode and form small In2O3 crystals, which are thermodynamically stable. By increasing time, these small crystals grew and converted to various forms depending on the available conditions. Some of these conditions include factors such as pH of the electrolyte solution, the super- saturation degree, the penetration of unstable nucleuses into the stable crystal surface, and surface energy [9]. In this study, the growth process can be represented by the following relationship: InCl2 + H2O2  In3+ + 2HCl +O2 + 3e H2O2 + 2e  O2- + H2O

(2)

2In3+ + 3O2-  In2O3 (Nanostructures)

(3)

(1)

Studying the PL spectra is an effective technique for evaluating both the In2O3 defects and optical properties. It is known that the bulk of In2O3 is not emitted at room temperature [24], but its nanostructures have this ability at room temperature [25] and emitted in the visible and ultraviolet region of the electromagnetic spectrum. Although many reports have been provided about PL of In2O3 nanostructures, but its mechanism has not been fully understood yet [26]. Crystalline defects such as O vacancies in In2O3 structure play a major role in the mechanism of PL due to formation of new energy levels in the electron band structure of semiconductors. Figure 3 shows PL spectra of un- and Zn-doped In2O3 nanorods. According to this figure, 2% Zn- In2O3 specimen has two emission bands in positions of 418 nm and 455 nm that both of these bands are located in the violet region of the visible spectrum. These two emission bands are considered as near band edge emissions (NBE). Two other emission bands are observed in the positions of 492 nm and 519 nm that are in the green region of the visible spectrum. Crystalline defects have been known as their origin that 6

O vacancies are mainly considered here [27]. Another band, which has a lower intensity and a larger distance than the rest, is located at 689 nm in the red region of the visible spectrum and is an emission of deep level. It is also due to the presence of O vacancies in the crystal lattice of In2O3 [28]. Emission bands show a red shift in the doped specimens compared with the undoped specimen that suggesting the reduction in the emission band gap energy after doping with Zn. Its reason as mentioned in the section of diffraction patterns can be attributed to replacement of some of Zn atoms instead of In and the formation of partial zinc oxide (ZnO) compound. As we know, the band gap energy of ZnO is less than In2O3. Therefore, this displacement is consistent with the theory rule and is reasonable in terms of moving towards greater wavelengths [29]. Figure 4 shows the absorption spectrum of un- and Zn-doped In2O3 nanorods with different concentration of Zn. For all specimens, the absorption edge is in ultraviolet region and the absorption intensity is decreased by shifting towards larger wavelength. The presence of the absorption edge in this region causes larger band gap energy than the emission band gap energy of nanostructures, because the band gap energy obtained from the analysis of the absorption spectrum, called the optical band gap energy, is usually larger than the emission band gap energy of the same substance. Its reason can be attributed to transitions from outer bands in interactions of carriers during absorption of photon compare with the transition from the inner bands during photon emission from the semiconductors electron band structure. The undoped In2O3 nanorods have 88 % absorption and the specimens doped with Zn have 73 % and 53 % absorption, respectively. These results show that the absorption percentage is reduced by adding Zn dopant. In order to estimate the optical band gap energy of the nanostructures, Tauc plot method has been used. In this method, the following equation known as the Kubelka-Munk equation model is used [30] √αhν = B(hν-Eg(

)4(

Where, α is absorption coefficient, h is Planck's constant, ν is frequency and B is a constant. Using this equation and Fig. 5, which shows the amount of energy (hν) versus (αhν)2, (α is absorption coefficient) according to the Kubelka–Munk model. As Fig. 5 shows, the Zn dopant reduces the band gap energy of In2O3 nanostructures. Its reason as mentioned in the section of the PL analysis is creation of small amounts of the ZnO compound after doping In2O3 nanostructures with Zn. These values also show a red shift compared with the 7

band gap energy of bulk In2O3. For this shift, there are two proven reasons. The first one is nanostructure size and shape and second one is the presence of crystalline defects [25] such as O vacancies in In2O3. The first one points to an increase in the surface to volume ratio and the second one is also seemed obvious according to the results of the PL analysis. Therefore, this conclusion is also consistent with the results obtained from SEM images and PL analysis. In order to investigate the electrical properties of films, I-V characteristics of deposited In2O3 films under dark and illumination (different light) conditions were performed and represented in Fig. 6. All samples under illuminated conditions showed lower current at the same voltage as compared with the dark condition. This behavior previously to be observed and reported for ZnO nanowire by Soci et al [31]. It can be suggested this is related to the interaction in grain boundaries of In2O3 thin films. In illumination condition, because of O desorption by surface holes, empty state at grain boundaries increases and condition for much trapping of electrons was provided. This phenomenon increases the barrier height at surface of thin films and lower carriers can be transmitted at the junction. Hence, photocurrent decreases and resistance is increases [32, 33]. In addition, these plots show a turning on voltage that indicates of the Schottky behavior by FTO/In2O3/iodide/Pt structures for all samples. Mott-Schottky plot is a good and straightforward tool for identification of conductivity and carrier concentrations in semiconductors [34]. This plot can be obtained by recording C-V characteristics of thin films at ambient conditions as shown in Fig. 7. Positive slope of fitted lines on Mott-Schottky plot indicated of n-type nature of all In2O3 thin films [35]. Slope and Intercept of these fitted lines on Mott-Schottky plot represent flat band voltage and donor concentration of In2O3 thin films [36]. These amounts are extracted and listed in Table 1. With Zn doping flat band voltage and donor concentrations of In 2O3 thin films are increased. Previously, increases in carrier concentration with low concentrations of Zn (in other methods) atoms and other metal dopants for In2O3 structures were seen and reported [37-41]. Increases in carrier (donor) concentration probably are due to the higher substitution (state) of Zn atoms in comparison of interstitially (state) of Zn atoms in crystal structures of Zn-doped In2O3 thin films [38]. To investigate the photocurrent ability of the deposited thin films, a periodic light excitation test has been used. Figure 8 shows the time-current plots for the un- and Zn-doped In2O3 nonorods. For un-doped specimen after exposure to light, the spike anodic photocurrent 8

appears. This current is generated as a result of generation of electron-holes in the interface or the depletion layer of semiconductor film and electrolyte solution (iodide). The timedependent photocurrent decay appears immediately and this continues until reaching to the steady state. In fact, this steady state is equilibrium between the maximum photocurrent and the recombination of carriers current. By comparing the photocurrent of un- and 2% Zndoped specimens, it is easily cleared that the rate of recombination in the un-doped specimen is more than the doped specimens. In the case of 2% Zn-In2O3 specimen, the photocurrent and the life time carriers have been increased substantially. This significant increase indicates the presence of trap sites caused by structural defects. In other words, a part of carrier, which has been created by light (photo-induced carriers or electron-hole pairs), has been trapped by the trap sites that reduces the possibility of recombination and increases the carriers lifetime. Extra carriers have been placed in the conduction and valence band to neutralize the electric field and photo-conductive is increased by increasing the trapped carriers. This phenomenon is indicated that 2% Zn- In2O3 specimen has high density of defect such as O vacancy that EDS and PL results also shows this Deficiency. After cutting the beams of light, photocurrent is rapidly diminishing due to direct recombination of carriers (electron-hole pairs), and carriers trapped in the trap sites are released due to thermal excitation and in a period of time, they reach to the values corresponding to the no light condition [42, 43]. Generally, absorption and desorption of O have a very important role in the transition of carriers. At the time of illumination, electron-hole pairs have been generated and the holes have been transmitted on the surface and causes desorption of O adsorbed on the surface and this decreases the depletion region width and increases the density of free carriers. By cutting off the light, O is re-absorbed that reduces the density of free carriers. Therefore, it can be concluded that photocurrent behavior of In2O3 thin films are competition between surface desorption-adsorption of O and carrier photo-excitation processes [33].

4. Conclusions Un- and Zn-doped In2O3 nanorods thin films were deposited using the electrochemical deposition method. Adding of Zn dopant showed a shift towards smaller angles in the position of diffraction patterns peaks that it is because of applying the stress on the crystal lattice of In2O3 by Zn atoms. The In2O3 thin films showed nanorods shape that addition of Zn impurities changes just their size. Optical and emission band gap energy of 9

nanostructures were estimated using the results of the data analysis of PL and absorption spectrum that the reduction was observed in both cases. The cause of this decline is the creation of small amounts of ZnO with band gap energy less than the In2O3. The results of photocurrent experiment have shown that at the time of optical stimulation, specimens has transient current due to the presence of superficial traps and recombination of generated carriers. Moreover, the doped specimens have the highest photocurrent ability and optical conductivity resistance. This phenomenon is in accordance with the results of PL analysis and confirms them.

Acknowledgements F. Jamali-Sheini gratefully acknowledges Islamic Azad University, Ahvaz Branch for their financial support of this research work. He also thanks to Advanced Surface Engineering and Nano Materials Research Center, Ahvaz Branch, Islamic Azad University, Ahvaz, Iran, for their instrumentation support.

10

References [1] Zheng M, Zhang L, Zhang X, Zhang J, Li G. Fabrication and optical absorption of ordered indium oxide nanowire arrays embedded in anodic alumina membranes. Chemical Physics Letters, 2001; 334(4-6); 298-302 [2] Sharma R, Mane R S, Min S-K, Han S-H. Optimization of growth of In2O3 nano-spheres thin films by electrodeposition for dye-sensitized solar cells. Journal of Alloys and Compounds, 2009; 479(1-2); 840-843 [3] Matei Ghimbeu C, Schoonman J, Lumbreras M. Porous indium oxide thin films deposited by electrostatic spray deposition technique. Ceramics International, 2008; 34(1); 95-100 [4] Montazeri A, Jamali-Sheini F. Enhanced ethanol gas-sensing performance of Pb-doped In2O3 nanostructures prepared by sonochemical method. Sensors and Actuators B: Chemical, 2017; 242(778-791 [5] Martínez M A, Herrero J, Gutiérrez M T. Optimisation of indium tin oxide thin films for photovoltaic applications. Thin Solid Films, 1995; 269(1-2); 80-84 [6] Matsunami H, Matsumoto S, Tanaka T. MIS silicon solar cells with In2O3 Antireflective coating. Japanese Journal of Applied Physics, 1977; 16(8); 1491-1492 [7] Dai Z R, Pan Z W, Wang Z L. Novel Nanostructures of functional oxides synthesized by thermal evaporation. Advanced Functional Materials, 2003; 13(1); 9-24 [8] Liang Y-C, Lee H-Y. Growth of epitaxial zirconium-doped indium oxide (222) at low temperature by rf sputtering. CrystEngComm, 2010; 12(10); 3172 [9] Epifani M, Comini E, Arbiol J, Pellicer E, Siciliano P, Faglia G, et al. Nanocrystals as very active interfaces: Ultrasensitive room-temperature ozone sensors with In2O3 Nanocrystals prepared by a low-temperature Sol−Gel process in a coordinating environment. The Journal of Physical Chemistry C, 2007; 111(37); 13967-13971 [10] Lin T, Ding X-y, Xu J, Wan N, Xu L, Chen K-j. Influences of doping and annealing conditions on the photoluminescence from In2O3 nanocrystals and Eu3+ ions co-doped sol-gel SiO2 films. Journal of Applied Physics, 2011; 109(8); 083512 [11] Korotcenkov G, Brinzari V, Cornet A, Morante J. Experimental and theoretical studies of indium oxide gas sensors fabricated by spray pyrolysis. Sensors and Actuators B: Chemical, 2005; 106(2); 563-571 [12] Pramod N G, Pandey S N, Sahay P P. Sn-Doped in2O3 Nanocrystalline thin films deposited by spray Pyrolysis: Microstructural, optical, electrical, and formaldehyde-sensing characteristics. Journal of Thermal Spray Technology, 2013; 22(6); 1035-1043 [13] Henríquez R, Muñoz E, Dalchiele E A, Marotti R E, Martín F, Leinen D, et al. Electrodeposition of In2O3 thin films from a dimethylsulfoxide based electrolytic solution. physica status solidi (a), 2012; 210(2); 297-305 [14] Gupta A, Cao H, Parekh K, Rao K V, Raju A R, Waghmare U V. Room temperature ferromagnetism in transition metal (V, Cr, Ti) doped In2O3. Journal of Applied Physics, 2007; 101(9); 09N513 [15] Sena C, Costa M S, Muñoz E L, Cabrera-Pasca G A, Pereira L F D, Mestnik-Filho J, et al. Charge distribution and hyperfine interactions in the vicinity of impurity sites in In2O3 doped with Fe, Co, and Ni. Journal of Magnetism and Magnetic Materials, 2015; 387(165178 [16] Ashida T, Miyamura A, Oka N, Sato Y, Yagi T, Taketoshi N, et al. Thermal transport properties of polycrystalline tin-doped indium oxide films. Journal of Applied Physics, 2009; 105(7); 073709 11

[17] Sun Y, Murphy C, Reyesgil K, Reyesgarcia E, Lilly J, Raftery D. Carbon-doped In2O3 films for photoelectrochemical hydrogen production. International Journal of Hydrogen Energy, 2008; 33(21); 5967-5974 [18] Xu J, Wang X, Li C. Electrochemical-Deposited In2O3 Nanocrystals for H2S detecting in air. Electrochemical and Solid-State Letters, 2006; 9(7); H53 [19] Xu J, Wang X, Li C. Electrochemical-deposited In2O3 nanocrystals for H2S detecting in air. Electrochemical and solid-state letters, 2006; 9(7); H53-H56 [20] Chu D, Masuda Y, Ohji T, Kato K. Shape-controlled growth of In(OH)3/In2O3 Nanostructures by Electrodeposition. Langmuir, 2010; 26(18); 14814-14820 [21] Ye F, Cai X-M, Zhong X, Tian X-Q, Jing S-Y, Huang L-B, et al. The electrical and optical properties of cu-doped in2O3 thin films. Thin Solid Films, 2014; 556(44-47 [22] ICDD. International Centre for Diffraction Data. Powder Diffraction File”(Newtown Square, PA 19073, USA), 1997; [23] Shannon R D t. Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides. Acta Crystallographica Section A: Crystal Physics, Diffraction, Theoretical and General Crystallography, 1976; 32(5); 751-767 [24] Gan J, Lu X, Zhai T, Zhao Y, Xie S, Mao Y, et al. Vertically aligned In2O3 nanorods on FTO substrates for photoelectrochemical applications. Journal of Materials Chemistry, 2011; 21(38); 14685 [25] Kumar M, Singh V N, Singh F, Lakshmi K V, Mehta B R, Singh J P. On the origin of photoluminescence in indium oxide octahedron structures. Applied Physics Letters, 2008; 92(17); 171907 [26] Shanmugan S, Mutharasu D, in s. Reference tools. Metallurgical and Materials Transactions A, 2011; 43(1); 6-9 [27] Wei Z P, Guo D L, Liu B, Chen R, Wong L M, Yang W F, et al. Ultraviolet light emission and excitonic fine structures in ultrathin single-crystalline indium oxide nanowires. Applied Physics Letters, 2010; 96(3); 031902 [28] Wang G, Park J, Wexler D, Park M S, Ahn J-H. Synthesis, characterization, and optical properties of In2O3 semiconductor Nanowires. Inorganic Chemistry, 2007; 46(12); 4778-4780 [29] Yousefi R, Cheragizade M, Jamali-Sheini F, Mahmoudian M R, Saaédi A, Huang N M. Influences of anionic and cationic dopants on the morphology and optical properties of PbS nanostructures. Chinese Physics B, 2014; 23(10); 108101 [30] Cheraghizade M, Yousefi R, Jamali-Sheini F, Saáedi A, Ming Huang N. Large-scale and facial fabrication of PbS nanorods by sulfuration of a Pb sheet. Materials Science in Semiconductor Processing, 2014; 21(98-103 [31] Soci C, Zhang A, Xiang B, Dayeh S A, Aplin D P R, Park J, et al. ZnO nanowire UV photodetectors with high internal gain. Nano letters, 2007; 7(4); 1003-1009 [32] Bondarchuk A N, Aguilar-Martinez J A, Pech-Canul M I. Effects of Zr dopant and sintering temperature on electrical properties of In2O3–SrO based ceramics. Ceramics International, 2014; 40(8); 11533-11541 [33] Huang S, Ou G, Cheng J, Li H, Pan W. Ultrasensitive visible light photoresponse and electrical transportation properties of nonstoichiometric indium oxide nanowire arrays by electrospinning. Journal of Materials Chemistry C, 2013; 1(39); 6463-6470 [34] Jamali-Sheini F, Cheraghizade M, Niknia F, Yousefi R. Enhanced photovoltaic performance of tin sulfide nanoparticles by indium doping. MRS Communications, 2016; 6(4); 421-428 [35] Ganjiani Z, Jamali-Sheini F, Yousefi R. Electrochemical synthesis and physical properties of Sn-doped CdO nanostructures. Superlattices and Microstructures, 2016; 100(988-996

12

[36] Jamali-Sheini F, Cheraghizade M, Yousefi R. SnS nanosheet films deposited via thermal evaporation: The effects of buffer layers on photovoltaic performance. Solar Energy Materials and Solar Cells, 2016; 154(49-56 [37] Warmsingh C, Yoshida Y, Readey D W, Teplin C W, Perkins J D, Parilla P A, et al. High-mobility transparent conducting Mo-doped In2O3 thin films by pulsed laser deposition. Journal of applied physics, 2004; 95(7); 3831-3833 [38] Jothibas M, Manoharan C, Ramalingam S, Dhanapandian S, Bououdina M. Spectroscopic analysis, structural, microstructural, optical and electrical properties of Zndoped In2O3 thin films. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2014; 122; 171-178 [39] Lee J J, Kim J S, Yoon S J, Cho Y S, Choi J W. Electrical and Optical Properties of Indium Zinc Oxide (IZO) Thin Films by Continuous Composition Spread. Journal of nanoscience and nanotechnology, 2013; 13(5); 3317-3320 [40] Frank G, Köstlin H. Electrical properties and defect model of tin-doped indium oxide layers. Applied Physics A, 1982; 27(4); 197-206 [41] Cox P A, Flavell W R, Egdell R G. Solid-state and surface chemistry of Sn-doped In 2 O 3 ceramics. Journal of Solid State Chemistry, 1987; 68(2); 340-350 [42] Grez P, Herrera F, Riveros G, Ramírez A, Henríquez R, Dalchiele E, et al. Morphological, structural, and photoelectrochemical characterization of n-type Cu2O thin films obtained by electrodeposition. physica status solidi (a), 2012; 209(12); 2470-2475 [43] Forsh E A, Abakumov A M, Zaytsev V B, Konstantinova E A, Forsh P A, Rumyantseva M N, et al. Optical and photoelectrical properties of nanocrystalline indium oxide with small grains. Thin Solid Films, 2015; 595(25-31

13

Authors Biographies

Asghar Shokohmanesh received her B. Sc. degree at the Islamic Azad University, Ahvaz Branch, Ahvaz, Iran, in 2010, and M. Sc. degree in 2015 for research activities in the Islamic Azad University, Ahvaz Branch, Ahvaz, Iran. Her research interest is optical properties of semiconductor nanostructures.

Farid Jamali-Sheini received his M.Sc. degree at the Islamic Azad University, Science and Research Branch, Tehran, Iran, in 1998. He earned his Ph.D. for research activities in Puna University, India on optical and field emission properties of ZnO nanostructures (doped and undoped) in 2010. He became the head of advanced surface engineering and nanomaterials research center in2014. He is an associate professor of physics at 2015, all in Islamic Azad University, Ahvaz Branch, Ahvaz, Iran. His research interests include optical, electrical, photovoltaic, photocatalytic, gas sensing and field emission behavior of semiconductor nanostructures.

14

figure captions: Fig. 1. XRD spectra of un- and Zn-doped deposited films. Fig. 2. SEM images and EDS spectra of a,b) In2O3 c,d) 2% Zn-In2O3 and e,f) 4% Zn-In2O3. Fig. 3. PL spectra of un- and Zn-doped In2O3 thin films. Fig. 4. Absorption spectra of un- and Zn-doped In2O3 thin films. Fig. 5. Tauc plot of a) In2O3 b) 2% Zn-In2O3 and c) 4% Zn-In2O3. Fig. 6. I-V characterization of a) In2O3 b) 2% Zn-In2O3 and c) 4% Zn-In2O3 Fig. 7. Motth-Schottky plot of In2O3 thin films. Fig. 8. Photocurrent plot of In2O3 thin films.

15

Fig. 1

Fig. 2

16

Fig. 3

17

Fig. 4

18

Fig. 5 19

Fig. 6 20

Fig. 7 21

Fig. 8

22

Table 1. Physical parameters of un- and Zn-doped In2O3 thin films.

Table 1 Physical parameters/Sample Conductivity

In2O3

2% Zn-In2O3 N n

4% Zn-In2O3 n

Flat band voltage (mvolt)

179 206

234

Donor

0.14 1.27

0.98

concentration

(10+17/cm3)

23